1. Field of the Invention
The present invention relates to a vehicle steering apparatus, and particularly relates to a power drive mechanism for making a pivoted steering column tilt to a desired angular position.
2. Description of the Prior Art
In a vehicle steering apparatus having a tiltable column, a steering wheel is attached to an upper shaft which is in turn operatively connected to a lower shaft through a universal joint. The lower shaft is pivoted on a fixed bracket attached to a vehicle, and the upper shaft is pivoted on an upper jacket through a movable bracket supported by the fixed bracket. If the movable bracket is moved, the upper shaft tilts together with the upper jacket so that the steering wheel attached to the upper shaft is held at a desired angular position.
There are some ways to move such a movable bracket. In U.S. Pat. No. 4,633,732 issued Jan. 6, 1987, one end of a link bar is connected to a movable bracket at an end thereof separated farther from a fulcrum, and the other end of the link bar is connected to a nut member engaging a lead screw. The lead screw is driven by an electric motor through a reduction gear so as to move the nut member in the axial direction of the lead screw as the lead screw rotates so that the nut member causes the movable bracket to perform angular movement through the link bar. The opposite ends of the link bar act as joints so as to convert the linear movement of the nut member into rotational movement of the movable bracket. Accordingly, there has been a disadvantage that the link bar is complicated in mechanism and mechanical errors are apt to be caused.